High efficiency magnetron



Dec. 16, 1947. P. SPENCER HIGH EFFICIENCY MAGNETRON 2 Sheets-Sheet 1 Filed feb. 1l, 1945 Dec. 16, 1947. P. l.. SPENCER HIGH EFFIClENCY MAGNETRON l 2 Sheets-Sheet 2 Filed Feb. ll, 1945` I I I I.. Il; Il I I Il Ummm@ LLLLE Patented Dec. 16, Y1947 UNITED STATES PATENT OFFICE HIGH EFFICIENCY MAGETRON Percy L. Spencer, West Newton, Mass., assgnor to Raytheon Manufacturing Company, Newton, Mass., aV corporation of Delaware Application February 11, 1943', Serial No. 475,563

Claims (CL 315-1-39) This invention relates to a magnetron. and more particularly to one which has a plurality of possible oscillating modes, each.` determined primarily by the geometry of the internal strucL ture of the magnetron. A dev'ice of this kind is intended to oscillate in a predetermined principal mode so Aas to generate a predetermined iredueneyr Heretofore diiculties have been en countered in that additional modes of oscillation have occurred which introduced frequencies diifering somewhat from the desired output irequency. These additional modes have caused spurious oscillations to be generated, thus consuming energy and. reducing the ellciency and effectiveness of the device An object of this invention is to reduce to a minimum the tendency for such spurious oscillations to occur.

Another object is to increase the eficiehcy and effectiveness ci a magnetron of the foregoing type.

Awstill further object is to devise an internal structure for such a magnetron in which any possible spurious mode of oscillation has associated therewith another possible inode which tends to generate oscillations equal and opposite to those of said possible spurious inode. The yfr negoing and other objects ci' this invention 'will be best understood from the following description oi exemplications thereof, reference being had to the accompanying drawings, wherein:

Fig. i is a transverse section of a magnetron embodying my invention, taken along line I-l of Fig'. 2;

Fig. 2 is a longitudinal cross-section taken along line 2-'-2` of Fig. l:

Fig. 3 is a perspective view of one-'half of the anode structure of the arrangements shown in Figs. 1 and 2' cut along the line 3 3 of Fig. 1;

Fig'. 4 is a developed diagrammatic View of the faces of the anode sections of the arrangements as shown in the foregoing figures; and

Fig. 5 is a diagram similar to Fig.. 4, showing an alternate form of anode arm interconnection.

The magnetron illustrated in the drawings comprises an envelope I which is preferably triade of a block of conducting material, such as copper. This block forms the anode structure. of the magnetron, and has hollow end sections which are covered by caps 2 and 3, likewise of cony ductive material, such as copper. Between the hollow end sections of the block I is located a central bridging portion 4. The portion 4 is provided with a central bore 5 within which is supe portedsibstantially at the' center thereof a cathode 6 may be of the indirectlyeheated einde-coated tliernuonic type. The cathode is supported by apair` of cathode lead-in conductors I and 8 sealed through glass seals 9 and Il! mounted at the outer end of pipes Ii and I2 hermetically fastened within the walls of the block I adjacent the upper and lower hollow end sectionsr Light conducting shields 'l' and 8 may be supported adjacent the upper and lower ends of the cathode so as to prevent electron beams from being projected out toward the end caps 2 and. 3. A plurality of slots I3 extend radially from the central bore 5, and each of the slots terminates in a circular opening I4 extending through the bridging portion 4. In this way the anode structure is provided with a pluralityof wedge-shaped arms I522,-the faces of which cooperate as anode sections with the cathode 6.

When such a magnetron is placed between suitable magnetic poles 23 and 24 to create a longitudinal magnetic eld and the device is energized, oscillations are set up. These oscillations may be led out from the tube by means of a coupling loop 25 extending into one of the cylindrical openings i4, and having one end thereof 'fastened to the inner wall of said opening. The other end. of the coupling loop 25 is connected by a lead wire 26 which passes through a glass seal 21 mounted at the outer end of a pipe 28 likewise hermetically fastened through the wall of the envelope I. An additional conducting pipe, not shown, may be electrically connected to the pipe 23, and forms with the wire 26 a concentric line through which high freduency oscillations generated by the magnetron may be Conducted to a suitable utilization circuit.

Capacitances eXist between the side walls of each of the slots I3, the inner walls of the opening I4 constituting inductances. The anode, therefore, is so designed that the inductances and capacitances described constitute circuits which are tuned, and thus are resonant at a predetermined frequency at which the device is to be operated. The device is intended to operate so that each bore Iii and its adjacent arms form a vcircuit tuned to the frequency at which each of the other bores and its adjacent a'rrn's oscillate.

It has been found that in magnetrons of this general type there has been a tendency for' oscillations to be produced. not only in accord-r ance with the above desired mode, but also in various. undesired spurious modes. One particularly troublesome mode is that in which alternate anode arms form opposite ends of an oscillating circuit extending around the back of a pair of openings I4. As more fully described and claimed in my copending application, Serial No. 421,145, filed December 1, 1941, this spurious oscillating mode can be substantially eliminated by interconnecting the outer ends of alternate anode arms directly by low impedance paths by means of conductors set into the upper and lower tips of the anode arms. Both the principal and the spurious modes described above may be termed transverse modes.

Under certain conditions, the interconnections as described above introduce the possibility of a mode of oscillation occurring in a, circuit extending from one unconnected end of an anode face down along that anode face through one of the interconnecting conductors to an alternate anode face, and then up along that alternate anode face to its outer unconnected end. Such a mode of oscillation may be termed a longitudinal mode. If the dimensions of the longitudinal mode are very carefully chosen so as to make the longitudinal mode of operation exactly equal to the principal mode, the disadvantages of the presence of such an additional mode are considerably decreased. One arrangement whereby this equality may be produced is described and claimed in my copending application, Serial No. 425,071, filed December 31, 1941. However, this and similar arrangements often introduce undue complexities into a tube structure, and therefore it is desirable for many applications to produce a similar arrangement in which the necessity for equalizing the above-described longitudinal mode and the principal transverse mode is substantially eliminated. In accordance with my present invention, I produce this result by interconnecting the anode arms in such a way that with each possible longitudinal mode of oscillation is associated another longitudinal mode which tends to generate oscillations equal and opposite to those of the first-mentioned longitudinal mode.

In the arrangement shown herein, the interconnections are made substantially along the central portions of the anode faces by means of a pair of interconnecting conducting rings 29 and 30. Ring 29 electrically interconnects the anode arms I 6, I8, 20 and 22, while the intervening anode arms I5, I1, I9 and 2I have their faces provided with a slot through which the ring 29 passes freely so as to avoid electrical contact with said intervening anode faces. Likewise the conducting ring 30 is electrically connected to the anode arms I5, I1, I9 and 2I, while the faces of the anode arms I6, I8, 20 and 22 are provided with slots which permit the ring 30 to pass through without coming into electrical contact with said intervening anode faces. By these interconnections alternate anode arms are directly electrically interconnected, thus substantially eliminating the tendency for transverse spurious modes of oscillation to occur, as more fully described in my copending application, Serial No. 421,145.

Upon referring to Fig. 4, it will be seen that a path exists from the upper end of anode face I6 down to substantially the central point thereof along the conductor 29 to substantially .the central point of anode face I8, and thence to the upper end of said anode face I B. This circuit contains an appreciable amount of inductance and some capacitance, and thus constitutes a possible longitudinal oscillating mode. However, it will be also noted that a substantially equal and opposite path exists from the lower end of anode face I6 up to the conductor 29, along the conductor 29 to the anode face I8, and thence to the lower end of said anode face I8. This constitutes a possible longitudinal mode which tends to generate oscillations substantially equal and opposite to those of the previous oscillating mode described above. Thus, during operation, any tendency for either of these longitudinal oscillating modes to produce oscillations of any appreciable magnitude is counteracted and substantially eliminated by the equalfand opposite longitudinal mode associated therewith. An investigation of Fig. 4 will show that each possible longitudinal oscillating mode has associated therewith a substantially equal and opposite longitudinal mode in a manner similar to that as described above. Due to the foregoing construction, therefore, my present invention not only substantially eliminates the spurious transverse modes but also substantially eliminates the spurious longitudinal modes.

When two conducting rings 29 and 30 are utilized so as to interconnect each alternate anode arm, said interconnections can be made only approximately along the center of the anode faces, since space must be provide-d for both of these conductors. If it is desired to interconnect the anode faces exactly at the central portions thereof, a single interconnecting ring 3| may be used in the arrangement as shown diagrammatically in Fig. 5. In this arrangement the ring 3I is electrically connected to the alternate anode arms I5, Il, I9 and 2l, while the faces I6, I8, 2E] and 22 are cut away along their central points so as to avoid electrical contact with the ring 3I. In this arrangement a more exact equality between the upper and lower longitudinal oscillating modes may be obtained. It will be noted, however, that such an arrangement does not provide for an interconnection between the alternating anode arms I6, I8, 2|] and 22, so that it might be considered possible for transverse oscillating modes to exist in connection with these non-interconnected anode arms. However, the ability of the transverse spurious mode to introduce deleterious effects into the device is dependent somewhat upon the ease with which the oscillations produced by such a transverse mode may be propagated around the tube. By eliminating such a, spurious transverse mode in connection with the anode arms I5, I'I, I9 and 2|, in effect a barrier is set up to the propagation of any oscillations generated by a spurious transverse mode associated with the arms I6, I8, 2E) and 22, so that for many applications the connection as represented by Fig. 5 may be satisfactory.

Of course it to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. For example, other anode configurations could be used in which a plurality of oscillating modes might be possible, and in which interconnections might introduce the possibility of spurious longi tudinal modes. In each instance, by utilizing the principles of my invention as enunciated herein, the entire arrangement may be made substan tially free of such spurious modes of oscillation, and thus the device may be caused to operate with high eiiiciency.

What is claimed is:

1. An electron discharge device comprising an electrode structure including a cathode and an anode, said anode having a plurality of anode faces of substantial length, a loop portion of said anode interconnecting each pair of adjacent anode faces, eachV of said loop portions forming a capacitance and an inductance constituting a tuned circuit which is adapted to have oscillations set up therein, and relatively low impedance means electrically interconnecting substantially the mid-points of alternate anode faces.

2. An electron discharge device comprising an electrode structure including a cathode and an anode, said anode having a plurality of anode faces of substantial length, a loop portion of said anode interconnecting each pair of adjacent anode faces, each of said loop portions forming a capacitance and an inductance constituting a tuned circuit whichv is adapted to have oscillations set up therein, and relatively low impedance means electrically interconnecting alternate anode faces, said means being connected to said alternate anode faces at points, each of which divides each connected anode face symmetrically.

3. An electron discharge device comprising an electrode structure including a cathode and an anode, said anode having a plurality of anode faces of substantial length, a loop portion of said anode interconnecting each pair of adjacent' faces of substantial length, a loop portion of said anode interconnecting each pair of adjacent anode faces, each .of said loop portions forming a capacitance and an inductance constituting a tuned circuit which is adapted to have oscillations set up therein, relatively low impedance means electrically interconnecting substantially the mid-points oi alternate anode faces, and means adjacent said electrode structure for producing a magnetic field about said cathode.

5. An electron-discharge device comprising a cathode, an anode structure spaced from and surrounding said cathode, a plurality of radiallydisposed anode arms extending inwardly from said anode structure, each pair of adjacent anode arms, together with that portion of said anode structure lying therebetween defining an openended cavity resonator communicating at the open ends thereof with end spaces formed in said anode structure, and a pair of closely adjacent conducting rings electrically connected, respectively, to alternate and intermediate anode arms.

PERCY L. SPENCER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,005,793 Lindenblad June 25, 1935 2,154,758 Dallenbach Apr. 18, 1939 2,247,077 Blewett et al June 24, 1941 2,250,698 Berline July 29, 1941 2,422,465 Bondley June 17, 1947 FOREIGN PATENTS Number Country Date 215,601 Switzerland Oct. 1, 1941 445,084 Great Britain Apr. 2, 1936 Certificate of Correction Patent No. 2,432,827. December 16, 1947.

PERCY L. SPENCER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 23, claim 2, before the Word symmetrically insert substantially; column 6, line 10, claim 4, after cathode and before the period insert n said electron discharge path, and transverse thereto; and that the said Letters Patent should be read With these corrections therein lthat the same may conformV to the record of the case in the Patent Oice.

Signed and sealed this 17th day of February, A. D. 1948.

. THOMAS F. MURPHY,

Assistant Uommzssoner of Patents. 

